Properties of dust in comet P/Halley measured by the Vega-2 three-channel spectrometer

Abstract

Optical properties of cometary dust exhibit no substantial variations at distances from 100 to 15 000 km from the nucleus. Dust ejection can be approximated by cos φ where φ is the angle with the sun-nucleus axis. Phase functions of dust scattering at 10 wavelengths from 328 nm to 1.4 µm are obtained and discussed. Dust reflectivity is nearly constant in the range 0.3 µm to 1.8 µm. Vega-2 in situ measurements are analysed and compared with optical data. Phase functions calculated for Mie and Fresnel spheres fail to reproduce adequately the obtained data. More promising seems to be the approximation of rough spheres. Dust density was evaluated as 0.3 g cm−3 from comparison of the in situ data with our measurements. Dust velocities are approximated by the expression V g/V d =1 + (ϱr/b)1/2 with b= 4 g µm cm−3 obtained in our measurements. Total dust production rate equals 10 tons−1 and Q d/Q g ≈0.3 on 1986 March 9.